1. Field of the Invention
The present invention relates to a combination of a member made of rubber and a member made of aluminium alloy, in which corrosion of the aluminium alloy member that is liable to occur in contact relation to the rubber member can be reduced.
2. Description of the Prior Art
In the case where different kinds of metals, for instance, Al and Fe come into contact with each other and an electrolytic solution exists at the boundary contact surface portion, Al having a basic potential relative to Fe becomes an anode and resolves in the electrolytic solution. In order to prevent corrosion caused by contact between such different kinds of metals, the procedures such that 1 making an insulator intervene between the boundary contact surfaces of the respective metals, 2 preventing an electrolytic solution from entering the gap between the boundary contact surfaces, and 3 applying counter-potentials to the respective metals to eliminate a potential difference, are employed.
As this contact corrosion occurs at a contact portion between different kinds of metals, it is quite natural to consider that it cannot be generated between rubber that is deemed as an insulator and metal. For instance, while it is known that rust is liable to be produced on a body steel sheet at the location where rubber parts for motorcars such as weather strips (members for blocking gaps in a vehicle body), bonnet seals or the like are disposed, the cause of rusting was believed simply to be because at the location where rubber parts serving as seal members are disposed, water is apt to stay and hence a corrosive environment is produced.
By the way, in recent years with the aim of realization of a light weight of a vehicle body, an excellent performance and a low fuel consumption of a motorcar, examples of formation of members such as bonnets, engines and the like of aluminium alloy having a density ratio of 1/3 with respect to Fe have been increasing. What becomes an issue in the conversion into aluminium alloy of the members to be used for motorcars, is corrosion generated in a contact relationship to different metals such as Fe or the like. In the cause of investigating the problem of corrosion of aluminium alloy, the inventors of the present invention have reached the knowledge that corrosion of aluminium caused by existence of an electrolytic solution would proceed especially in a contact relationship between rubber containing carbon black and aluminium alloy (including also metallic aluminium). The present invention has been worked out under the above-mentioned technical background.